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Liu et al. Microstructures 2023;3:2023009 https://dx.doi.org/10.20517/microstructures.2022.29 Page 3 of 11

accompanied by a relatively low η of 69% owing to large polarization hysteresis for the first-order
[25]
antiferroelectric-ferroelectric phase transition under high electric field . Therefore, a practical approach is
urgently required to simultaneously regulate the W and η of NN ceramics. In this work, CaZrO (CZ) was
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introduced into NN ceramics to not only destroy long-range antiferroelectric ordering but also remain large
antiferrodistortion. On the one hand, the enhanced local random field along with the strengthened
dielectric relaxation behavior would benefit the high η owing to the fast response of nanoclusters to the
external electric field. On the other hand, the existence of large oxygen octahedron tilt would hinder the
formation of long-range ferroelectric ordering under electric field, leading to the delayed polarization
saturation process. Combined with the fine grains, dense and homogeneous microstructure, ergodic
relaxation behavior, and delayed polarization saturation, a high recoverable energy storage density of
~5.4 J/cm and a large efficiency of ~82% can be realized in 0.85NaNbO -0.15CaZrO ceramics at an
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ultrahigh breakdown electric field of ~68 kV/mm, showing a great application potential in the field of
dielectric energy storage.
MATERIALS AND METHODS
Sample preparation
The ceramics of (1-x)NaNbO -xCaZrO ((1-x)NN-xCZ, x = 0-0.15) were prepared by the conventional
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solid-state reaction process. The raw materials of Na CO (> 99.9%), CaCO (> 99.5%), Nb O (> 99.9%), and
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ZrO (> 99.9%) were weighed according to the chemical formula and mixed by planetary ball milling for 8 h
2
using ethanol as ball milling media. The mixed powders were calcined at 850 °C for 5 h after drying. Then,
the calcined powders were ball-milled again by high-energy ball milling (700 r/min for 8 h) with ethanol
and 0.5 wt% PVB binder. Afterward, the powders were pressed into pellets with a diameter of 8 mm and a
thickness of ~1 mm. The pellets were sheathed using the corresponding calcined powders in crucibles and
sintered at 1370 °C for 2 h. Finally, the sintered ceramics were polished to a thickness of ~0.1 mm with a
diameter of ~6.5 mm and coated with silver electrodes with a diameter of ~2 mm, which were fired under
550 °C for 30 min to measure their electrical properties.
Structural and performance characterizations
The high-energy synchrotron X-ray diffraction (SXRD) data was measured on the 11-ID-C beamline of
advanced photon source. Powder neutron diffraction data were collected at CSNS (China Spallation
Neutron Source, MPI) using time-of-flight powder diffractometers. The diffraction data refinement was
taken by the Rietveld method on software GSAS II. Temperature- and frequency-dependent dielectric
properties were carried out using an impedance analyzer (Keysight E4990A, Santa Clara, CA). Domain
morphology and selected area electron diffraction (SAED) were observed on a field-emission transmission
electron microscope (TEM, JEM-F200, JEOL, Japan) at an accelerating voltage of 200 kV. High-angle
annular dark-field (HAADF) atomic-scale images were obtained using an atomic-resolution scanning
transmission microscope (STEM, aberration-corrected Titan Themis 3300), and the polarization vectors,
polarization magnitude, and polarization angle maps were calculated by customized MATLAB scripts. The
morphology of grains was filmed using a scanning electron microscope (SEM, LEO1530, ZEISS SUPRA 55,
Oberkochen, Germany). Energy-storge properties of ceramics were investigated by a ferroelectric analyzer
(aix ACCT, TF Analyzer 1000, Aachen, Germany).

RESULTS AND DISCUSSION
Figure 1A shows the temperature-dependent dielectric permittivity (ε ) of (1-x)NN-xCZ ceramics at 1 MHz.
r
Pure NN is determined to be antiferroelectric P phase structure at room temperature accompanied by two
dielectric anomaly peaks at 130 °C and 370 °C, representing the transitions from antiferroelectric P phase to
incommensurate (INC) phase and INC phase to antiferroelectric R phase, respectively [26-28] . With the